The overall objective of the proposed research is to understand the pathogenesis and immunologic features of Marek's disease (MD) in chickens. Specific objectives include: 1) determining the relationship between genetic susceptibility and activation of T-cells as the mechanism providing transformable target cells, 2) investigation of factors, e.g. immune responses, which influence the development and maintenance of latency with MD virus, 3) characterization of molecular biological aspects of oncogenic and nononcogenic MD viruses and various virus-host cell interrelationships and 4) further characterization of immunological effector systems and target antigens important in resistance and vaccinal immunity.